You're never going to be right nine times out of ten.

In this business (investing) if you're good, you're right six times out of ten. You're never going to be right nine times out of ten.

- Peter Lynch

In investing, always mistakes are going to happen. This happens because there are always some variables as the investor is looking for the future which is always uncertain and there could be surprises and mistakes which the investor may have not factored in. As the objective is to minimise the mistakes and maximise the profits, doing the proper spade work before investing delivers the results.