Is it necessary to have an investment manager whenever we want to invest?

First of all we have to analyse where we want to invest and how much we want to invest.
In my personal opinion if I want to invest I will do it by myself to gain knowledge and experience.
Secondly it also a difficult to find a good investment manager. There are many persons available on the market who claims to be a good investment manager but who should we can trust on and why?
However if someone thinks he/she is unable to make correct decision, Investment manger can be a good option. Following factors should be considered before selecting the fund Manager:-

1. we should select a person who have variety of investment portfolio
2. It is also very necessary to identify which kind of investment you want to do
3. Make sure that investment adviser is trust worthy.
4. Investment manager should be easily accessible at all the times
5. Consistently observe the performance of investment manager