My mother was a firm advocate of the Little White Lie, that nifty social convention that allows you to get away with a dishonesty provided the intention is kind. Sometimes you don't want to hear that your boyfriend is unpleasant, that your drunken karaoke voice is not as mellifluous as it sounds to your own ears – or that your latest western blot looks as if it's been dragged across a car park by a hungry urban fox (“Why don't you get another replicate to bolster that promising finding?”, being the correct tactful response in the latter situation).

Our lab is hiring a new PhD student and, as part of the ritual, we are all required to take each supplicant for lunch out of earshot of the boss, Dr Keen. The idea is, of course, that the wanna-be can get the real lowdown on the prospective boss. But of course it's good for the lab to check out the wanna-be in turn, to make sure he or she is the sort of person one can live with for the next three or so years.

Now, I've been in the game for a number of years, but I'm not the most experienced post-doc in the lab. No, that dubious honour falls to Endosome Eddie. This is his third postdoctoral stint, and it shows. Eddie wears his careworn years all over his posture: he doesn't so much walk as slouch, and when he takes a seat at the beginning of lab meetings, he collapses into the chair with a heavy sigh and a glance at his watch that seems to say, I can't believe I've only been wasting my time for ten seconds. It seems like a lifetime. And the more months that go by with Eddie failing to land a permanent position, it goes without saying that when it comes to the topic of career prospects for promising young scientists, Endosome Eddie is not the person you want to get started.

So I wasn't too surprised when Dr Keen took me aside before lunch and murmured, “I can count on you, right?”

“Of course you can. Er, for what exactly?”

“With the candidate,” he said, giving me a significant look. And then, a brief hopeful glimmer: “I don't suppose Eddie's too busy to join you all?”

“No, he seemed especially eager.” If there's one thing Eddie likes more than a free lunch, it's the chance to unburden his opinion of the scientific profession onto an innocent, unblemished specimen.

Dr Keen sighed. “That's a pity. Well, in that case, can you please try to at least…”

“Shut him up?”

“I was going to say, temper his opinions with some counter-balancing positivity. But I think we understand one another.”

With a pat on the shoulder, he left me with fifty quid for lunch and a sense of mounting futility. Trying to stop Eddie in full flow was like trying to prevent a carboy full of ethanol with a broken stopcock from depositing its full four litres of liquid onto the lab floor – and trust me, I know what I'm talking about here. The floor has never looked cleaner; but that's another story.

So I collected the candidate from Dr Keen's office at the appointed time and met the rest of my labmates over at Luigi's for some pizza and plain talking. I ordered Eddie's favourite toppings in a desperate bid to keep his mouth full at the crucial moments – for I could immediately see trouble brewing. The candidate was lovely: bright, articulate and brimming with ambition and enthusiasm for the trade – in short, a perfect victim meal for Eddie's jaded palate. I tried very hard to steer the group's conversation to safe topics: the best places to live in London, the candidate's undergraduate research project, the unseasonably cold spring weather. But in the end, it was inevitable:

“So,” Eddie drawled, after swallowing a particularly large chunk of pizza with gusto. “What are your…career plans?” He made the last two words sound like a terminal disease.

“Oh, the usual,” she replied, eyes lit up with passion. “I'm going to start my own lab and make real inroads into understanding the mechanisms of cancer.”

There was an uneasy silence, and the shuffling of a few feet. I opened my mouth to reply, but Eddie cut me off.

“I'm afraid you might find that it's not actually as straightforward as you might have been led to believe,” he said. Behind his back, one of my colleagues rolled his eyes in a here we go sort of way.

“Of course not,” the candidate said hastily, with a nervous laugh. “I'm not saying I'm going to single-handedly cure cancer” – which was actually a refreshing change from the usual candidate delusion, I thought to myself. “I mean I'm going to chip away at it along with everyone else, make my own modest contribution.”

“That's not what I meant,” Eddie said. “I meant actually getting the chance to start your own lab is a tremendously long shot.”

“There are a few really great shows opening in the West End this weekend,” I said weakly. “How long are you in town for?”

The candidate, unfortunately, was still focused on Eddie. “Well, of course it's not going to be easy,” she said. “I need to work really hard, and I'm sure there's a lot of luck involved too.” But an element of uncertainty had crept into her voice.

At this point, speaking of luck, Eddie's mobile went off and he excused himself.

The candidate turned to the rest of us. “Is he right? Is it such a long a shot that it's not even worth trying?”

As the second-most senior person in the lab, everyone else seemed to be looking at me. And in that brief moment before responding, a number of things flashed through my head. I thought about the last lab head job that had been advertised in our building, and how there had been three hundred applications. I thought about the state of the economy, and the rumours flying around about upcoming cuts for science funding and grants. I thought about the even scarier gossip that had started circulating of late, that universities were going to start making some lab heads redundant to cut costs.

And I also thought about my mother. Although she wouldn't approve of me disillusioning this bright young individual, she also wouldn't want me to lie. But there were ways of doing it, ways that Eddie could never understand.

“Of course not,” I finally said, and – the spell broken – the rest of my labmates started nodding encouragingly. “Sure, it's going to be tough, but none of us regret our decisions.” (This, strictly speaking, was true, now that Eddie had left the table.)

So we gave her the real lowdown that afternoon: not about Dr Keen's unearthly talent for sneaking up behind us at the precise moment we were grabbing a five-minute Facebook break, but about the scientific profession. Yes, many are called but few are chosen, and yes, times ahead promise to be leaner than ever. But the thing about a PhD, and even a short post-doc thereafter, is that it is the gateway not only for an industrial career, but for all sorts of other really interesting science-related but non-research jobs – publishing, consulting, patent law and science communication to name but a few. Studies have even shown that people with scientific training tend to earn more in non-science jobs than those who haven't. Also, doing a PhD trains you to think critically and gives you a host of transferable skills. And in itself it's a tremendous achievement, one that you can be proud of for the rest of your life.

So yes, there are no guarantees, and all smart PhDs and post-docs know better than to expect a guaranteed job as a lab head at the other end. Quite a few of us will probably change careers – but that doesn't mean that the career will be less rewarding or that the scientific training was a waste. By the end of our chat, the candidate was upbeat, more convinced than ever that doing a PhD was a win-win situation.

Dr Keen ambushed me later while I was doggedly repeating that ugly western blot.

“So, how did it go?” he asked. “Great – I think she'd be perfect for our lab.”

“Me too. And did she get a good impression of us, too?”

“Fortunately,” I said, “Eddie was called away by a phone call before he could do much damage.”

Dr Keen winked at me and said, “Yes, I know,” before striding off with a spring in his step.