You definitely need a strategy, no way.

On the other hand why is someone spending time on strategy when he/she will then act day-by-day?

One: what is called a strategy, usually is not – I suppose people have got no ideas on what strategy is.

Two: strategy can be changed once things have been set into motion – forget this and you may find yourself in dire predicaments, i.e., better not to have a strategy at all.

Yes, without a Strategy failure is probable; remember, your strategy has to be modified when necessary.