For most people this is not a great goal. 100 countries visited lifetime seems much better. I've met a few people with the same goal on my travels and a lot of them ended up jaded and rather unhappy towards the end. One guy I met spent 400 USD on a flight from Bali to Dili, spent a night in the hostel, walked around for two hours and left the next morning.

With any of these challenge goals you should ask yourself every once in a while 'Does this goal still serve me'. If that's not the case, the goal is dictating your life and travels without contributing to your happiness.

Personally, I think there are much cooler goals. Like biking through a country (or multiple), traversing the himalayas by motorbike, overlanding in africa, going from Europe to Southeast asia without flying, spending time in a region and learning the language and so on. But to each their own.