(This post is part of a bigger list of rules that I have found helpful for thinking about a career, and beyond. See this post for an explainer).
This rule has carried me through both my academic and non-academic lives for two decades, and it's still going strong.
Having alternatives gives you peace of mind, and in my experience, peace of mind is what allows you to take that occasional extra risk that's necessary to excel at what you do, to innovate at a higher pace than what you'd be comfortable with in the absence of alternatives.
Having alternatives does not mean not being 100% committed to what you currently do. It simply means having that deep trust that tells you "even if things go totally wrong, I'll be fine. There will be something else".
Some people have that trust even when there are no obvious alternatives. I envy those people. Fundamentally, I think they are right. In the end, it'll be alright. In my dreams, I am as cool as that :-) But in my real life, I am not, and I love having a backup plan.
For somewhat random reasons, my backup plan has always involved web technologies. It's something I began playing with as an undergrad, and that I kept getting better at over the years, out of a fascination for the rapidly expanding web and all its implications. The day I realized these skills have serious market value was the day I became a much more relaxed and focused student of biology. I studied biology for the love of plants and animals, and I did my PhD in theoretical biology because I wanted to very deeply understand the most important idea in the world (evolution). I absolutely did what I loved, but it was also absolutely clear that the market for this kind of knowledge was virtually non-existent, and that having an alternative was necessary.
Asking people to reflect on alternative career paths is some kind of taboo - often used as a euphemism to suggest that they're not good enough at what they're doing. This is not at all what I mean when I invite people to reflect on alternatives; quite the opposite. Realizing that you have options is a great relief and brings back a sense of control. And because of that, it will most likely improve your ability to concentrate on what you're currently doing, enabling you to do the best work you possibly can.