Just don’t, it’s crazy!
Unless you’re seeing your trip as a holiday or you really have something to go home to, keeping yourself open to all options is the best way to experience things. I try not to book too much stuff up, or have any commitments.
This is not the same as not having a plan. I find a plan allows me to see everything I want, in the most cost-effective and hopefully most enjoyable way. Planning ahead allows you to find your favourite way to approach locations, and to make sure you squeeze everything you want in. Certainly in Vietnam I had a calender worked out for each day, and I’m so glad I did, I got to fit it all in, without (too much) stress! In countries that have limited time visas this is vital. But don’t lock your plan in, it’s not set in stone, so when you meet the coolest guys, or the love of your life, and you hear about somewhere new and secret, adjust that plan and check it out!
Talking to other travelers is the best way to work out where to go next, better than any guide book or website, these travelers were there only days ago, they know what’s going on, so ignore them at your periL.
I’ve met so many people that have regretted having their flights booked, and none that regret not booking them before. Sure we might end up paying a bit more, but for the freedom it allows, it’s definitely worth it.
And most importantly, never book that return flight! You never know where you’ll end up, or be flying to.