One of the things I work on is the nucleation of crystals. Nucleation is how crystals start to form, and so control over nucleation basically means being able to start a crystal growing where we want and when we want. We scientists have tried really quite hard to do this, for decades, and to be honest we are still pretty rubbish at it. We still can’t predict what we need to do to make a crystal on command. Sometimes nothing happens when we want a crystal to nucleate, other times when we want one crystal to form, instead we get dozens. It is a bit of a tale of woe.