Can i simply buy a counter without careful thinking of it?

Searching for a company and decided to invest in it is a tough decision an investor should takes as once invested, it will physically influence the investor emotion and arguments. 

When he/she invested in the company, the price goes down for example he/she sells. 

After selling, the price goes up. Will he/she be thinking of buying back? 

After he/she bought back, price goes down. Will he/she be thinking of selling off?

How often his/her emotion is shaken by stock price? 

Will he/she be losing all of his/her capital?