“I live my life day by day, and that’s how I continue to live it.”

Naomi Campbell

“The worst was when my skirt fell down to my ankles, but I had on thick tights underneath.”

Naomi Campbell

Edit: repeat.

I think the person who takes a job in order to live – that is to say, for the money – has turned himself into a slave.
Joseph Campbell

That’s why you should always respect and admire those on benefits 😀

As I see it the possible outcomes of having a life plan are these.

1. You achieve your planned objectives, and you’re disappointed by how it feels.
2. You fail to achieve your planned objectives, and you’re disappointed by how it feels.
3. You achieve your planned objectives, and you’re happy with how it feels.

So you’ve got a 1 in 3 chance of success! But who knows, even if you achieve number 3 and you think you’re finally happy, you might have missed loads of other, better, different stuff whilst you’re narrow-mindedly pursuing your plan, which was probably flawed in the first place.

I think that is a great description of why plans work so well for some people. It’s possible to be clever and academic and find life easy as a set of clear targets/exams etc. Here’s the criteria, here’s exactly what you need to achieve. Tick, tick, tick. It’s hard work, but there’s little risk or uncertainty so, is it really hard work?
There is much to be gained from risking failure.

Scientific research is the essence of risk and uncertainty, though. It’s a long way past taking exams. You’re trying to establish new knowledge and understanding, even new thought processes in the most successful cases. The hardest of work – and v risky if you’re truly ambitious. [The science that the OP was talking about in the context of his brother also happens to be very hard work in the plain English definition – along with molecular biology it’s probably the most labour intensive science there is].

This is mitigated to some extent when you’re doing your PhD and postdoc, as you’re working under someone else’s vision. Ask anyone here if there was risk and uncertainty in their PhD, though, or possibility of failure, and they’ll think you’re being funny.
Things really open up when / if you take the next step to do your own research. Here’s a desk, there’s your (empty) lab – now make something happen with it. Many an academic’s ‘life plan’ has gone off the rails at this point.

As I see it the possible outcomes of having a life plan are these.

1. You achieve your planned objectives, and you’re disappointed by how it feels.
2. You fail to achieve your planned objectives, and you’re disappointed by how it feels.
3. You achieve your planned objectives, and you’re happy with how it feels.

So you’ve got a 1 in 3 chance of success! But who knows, even if you achieve number 3 and you think you’re finally happy, you might have missed loads of other, better, different stuff whilst you’re narrow-mindedly pursuing your plan, which was probably flawed in the first place. #1 is a great point, and just as important as #2. If you’re on rails to get to some career / life objective – what do you do when you get there?
If you’ve no balance in your life they’ll be trouble brewing either way.