it is easy only when you are saying it but when it comes down to actually doing it, you need a lot of experience to notice where exactly is the top and were exactly is the dip's bottom to buy back.
yeah after it happens you can open the charts and see where the top and bottom had been but when things are happening by that time there is no way you can predict it without enough experience and analysis.
so it is not easy at all. which is why holding long term is the way to go for most people
Its very easy. Fact. But it will take lots of time wathing the charts to know when to sell or not. If you dont have the time, then hodling is the best thing to do.