Do you usually plan things out or just go with the flow?

I'm going backpacking in three weeks to Japan, China and Mongolia for two months and a half. My first stop is Tokyo, Japan and I already book my first six nights there and I'm going to be spending 28 days in Japan. After Tokyo, I did not book the rest of my stay because I thought I will go wherever it takes me and I did not book any nights in China (I'm going to be spending a month there as well). Mongolia is the only place where I book at least 7 nights out of my two weeks stay there because I'm going to be there on a high season. The thing is... It's my first time backpacking and I've never done this before. So I'm just curious, do you guys plan your whole itinerary (Hostels booked, the places to be visited...) or you just go with the flow (Not knowing where you are heading say in two days) ?

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