do not put all eggs in the same basket.
I have read this one somewhere in a different thread and it is really true. If you put it all in one basket you might lose it all with just a blink of an eye.
Does this also apply on wallet? I mean, is it better to split our btc into different wallets instead of using one main wallet which collect all the money we have?
Well theres a case to put in a few wallets. But risk of losing your btc from wallets is lower. There is only the counterparty risk but established wallets should be relatively safe. The diversification makes more sense for investments as you can lose due to failed investment or counterparty risk so... make sure u diversify