Never finished a book in my life (26M). What should be my first one?

I'm 26M and I've never actually finished reading a book from start to finish.

I spend a lot of time on business, tech, and learning online, but I've realized I'm missing out on the depth that books can provide.

If you could recommend just one book for someone like me, what would it be and why?

I'm mainly interested in books that can genuinely improve the way I think, make decisions, or approach life and business. I'm open to fiction too if you think it's a great place to start.