We've talked a bit on the strategy, here we will go a deep further so you can understand why some strategies work, why others don't and why some strategies are harder then others.

Example1: Let's say you are NE versus human on TR. We will skip the early game, and just say that you will be playing on DH+Naga and a few archers, teching to t3 for bears/dry. He on the other hand will scout you and see that you will be making bear/dry. He was going to play a few footmans in start with AM and then Naga. Now there is something you need to know. Choosing a strategy, playing as best as you can, you can still lose. You have to understand that every strategy has a counter, some have easy, others - hard. The human can decide to make 1-2 riflemans to protect himself from the dryad harras and then switch to caster/breaker/mortar. In this situation everything it's clear, expect for the right units. For example if he makes more sorceress and has a lot more slow then usual and switches the AM Blizzard together with Forked lighting and you have like 70% bears and 30% dryads in your army, I am sure your dryads won't have enough mana to abolish all of the sorceress's slow and blizzard/lighting will make it even harder on bears to kill the spell breakers. In this situation what you can do are two things: first one is to start making more dryads and the easier one is to take a few wisps with you(note: if they are 4-5 they won't be enough versus 2lvl lighting, 3 of them will die) so a good number of wisps is a must-have. The point here is that you can't play on one strategy whole game. Strategy is just for start and it is almost every game that you need to change it. It's just the way it is. You have to adapt to your opponent's strategy in order to have bigger chances of countering it.