Brown, of course, isn’t arguing that we should simply give up on our dreams. But if we return to that idea of the swimmer crossing from one bank to the other, it’s no good ignoring the currents pushing against us or believing that our force of will alone will overturn them – it is inevitable that you are going to be dragged off course.

If positive thinking can’t make us happier, what can? Brown argues that a healthier attitude to life comes from the Stoics, the ancient Greek philosophers who argued that we should actively and deliberately distinguish between the things that are within your power to change, and the things that aren’t – which we should learn to accept as a necessary part of life.

“I find myself doing this a lot that when something’s really bothering and frustrating me. I just think which side of the line is it on? Is it my thoughts and actions? Or is it something out there? It’s always something out there, it’s someone else’s behaviour. So then I think well, what if it was fine that that person is an idiot, or that my partner can’t handle stress well, or something like that – things that kind of end up having an effect on me, but actually, what if it’s fine, that that’s just their thing? It’s a very helpful thought, because then you take all the stress off yourself. You can then still work out how to help that person if you want, if that’s appropriate, but you kind of emotionally just disconnect from the pain of it.”

He gives an example of a game of tennis, but he says that same applies to any major challenge. “If you go into the game thinking ‘I must win’, that's out of your control. So if you start to lose, you feel like you're failing and then you become anxious… But if you go into a game of tennis thinking ‘I'll play as well as I possibly can to the best of my ability’ – that is under your control, and it doesn't matter if you start to lose – you won’t feel the frustration of failure, because you’re not failing, you’re still sticking true to your goals.”

Similarly, you can go into a job interview with the full knowledge that even if you perform your absolute best, the employer’s final decision is still beyond your control, and you can afford yourself a little compassion if you don’t make it. Brown says that this lowers our emotional “centre of gravity”, making us more resilient to life’s challenges. “[The Stoic’s] model of happiness was about avoiding disturbance.”

Brown also advocates the Stoic practice of premeditation every morning to prepare the mind for the day ahead. “It is, quite simply, spending a few minutes every morning, thinking about the day that lies ahead, and what the kind of traps are likely to be where you’re likely to let yourself down, and just anticipating them and thinking them through,” he says. This deliberate self-reflection – taken from a distanced perspective, when we are in a more rational frame of mind – reminds us that some things will be out of our control, and need not be the source of upset. At the same time it helps us to navigate the challenges that are within our control more wisely, so that we don’t just make the same mistakes again and again.

One of the best ways of achieving this, he says, is to leave the phone out of the bedroom. “It’s a little reminder that okay, instead of just browsing Twitter, I’ll think about what’s going to happen today and how I can meet those things in a more useful way.”