The nature of human is never get satisfied at any point if we are looking for $20000 then it will aim for more like $50K when it reaches then the expectation will keep on increasing so it is hard to decide when to sell our coins but we only can decide that when to sell since it is our coins we only can think more about ourselves than anyone.
You can also sell your BTC's when you are in the need of money.I will suggest you to keep holding your BTC's as long as you can because it has a very bright and positive future so it will reach new heights in coming future.