On the very first day of my PhD, I sat with all the other new students through a whole day of induction meetings.

Various people came to speak to us over the course of several hours; the safety officer, someone from the finance department, somebody else to talk about the monthly reports we were supposed to fill in...

But there was one that stuck in my mind. It was the "motivational speech" where we were told that we had been accepted onto a PhD program because, by definition, we were,

... the best of the best...

I'm sure it was meant to motivate us and give us confidence, but for me it had the exact opposite effect.

I was definitely not the best of the best. I hadn't done particularly well as an undergraduate, and I felt like I had bluffed my way onto a PhD program. Maybe these other people were the best of the best, but I was the impostor and I spent the next couple of years with a small but ever-present worry that I would be found out.

Worrying about what you don't know

I was always worried about what I didn't know. My maths wasn't that great by physicists standards, and there was a lot of fairly basic stuff that I had either forgotten or simply never learned in the first place.I would occasionally try to fill those gaps... I would get a book and leave it on my desk in the hope that the knowledge would enter my head by virtue of proximity, but of course it never did.

Background stress...

The fear of being found out added a level of background stress. It wasn't particularly bad... my life was perfectly comfortable and I wouldn't say that I was suffering, but there was certainly a slow erosion of confidence.

But this background stress stopped me working to the best of my ability. When I did an experiment, I never really believed that it would work, and so subconsciously I undermined my own effort by not doing things quite as carefully as I could.

Of course, this meant that things were less likely to work, which reinforced my negative beliefs, and the whole thing became a self-sustaining cycle of futility.

The realisation...

It was only in my third year of the PhD, after nearly quitting, that I realised something crucial...

Everybody has different skills and expertise. It did not matter that I had weaknesses and gaps in my knowledge, because there were other things that I was really quite good at. Other people weren't better or worse, they just knew different things.I had forgotten a lot of basic physics and maths because I didn't need it for my project and wasn't using it. But I had learned a huge amount about the experimental technique I was using, and knew the equipment as well as anybody.

I had become a specialist. An expert in one or two things. And so I decided to focus on that and not worry about how much I didn't know.I didn't have time anyway to fill in all the gaps, so there was no point worrying about it.

The thesis

When I came to write my thesis, I decided to focus only on material I knew and understood well. By focusing on my strongest areas, I could write faster and with more confidence.

There was always a risk that an examiner would ask me a question I didn't know the answer to, but I just took the view that this is my work, I am proud of it and I am happy to defend it, and if the examiner doesn't like it, I don't care.

With this attitude, I was able to relax and actually enjoy the writing process.

Get really good at something

The best of the best is meaningless. Everyone has different skills and strengths and weaknesses, and nobody knows or is good at everything.

So don't worry about comparing yourself to others, and don't worry about the gaps in your knowledge, because you can never fill all of them.But what you can do is get really good at a small number of things, know where your strengths lie, and focus on them instead.