These have been some of my most successful investments, but I'd still be confident in buying them.It's a common misconception that when a stock you buy skyrockets, the smart thing to do is sell it (or at least sell some of it) to lock in your profits. But the context matters. If the stock has increased sharply because the business is performing exceptionally well, it could still be a bargain.I have a few examples of stocks like this in my own portfolio. All three of these are up by 100% or more in just a fe ...