0 something that cannot be doubted: --
1 something that is very likely to happen: --
Joan will win - that's a certainty.
[ + to infinitive ] Joan is a certainty to win.
3 something that has no possibility of any other result; something that you know will happen in a particular way: --
There are few certainties in life.
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
Можем да го завършим стъпка по стъпка, колкото и дълъг да е пътят и не може да бъде завършен, колкото и кратък да е пътят, ако дори не маркирате отпечатъка си.