Ever wondered why you can ollie while rolling real fast but just can't ollie a ledge or stair set? Well, it's probably because you're scared.
The thing is, you just don't want to get hurt, no matter how much you want to land that trick! It's all in your head: there's no difference between ollieing 3 decks while moving and ollieing a 3 set (by the way, that's a good place to start).
You just need to make yourself do it. In that single moment before you make that ollie, you might feel this stab of fear in your chest. Even if you feel like you're going to fall, its always good to at least try to land the trick. You are going to fall, it's part of skating. So, if you're trying to ollie steps and you can't, its probably because you don't dare to do it. It's all mental, you just need to go for it!
And also, for your own safety, don't start out trying to ollie a 10 set. Please, you could hurt yourself, you'll look bad, and you don't know what kind of force you put on your feet in the landing process. This doesn't just go for ollieing steps or ledges, it goes for everything, from kickflips, to 360 flips, to even something as simple as an ollie, fear can always get in the way.
So, it's more than likely not that you're a bad skater, its just mental... so just skate