You control your self and not doing anything bad and copy other people wit good self control

Control of one's self; restraint exercised over one's self; self-command.

Self control is control of one's emotions, desires, or actions by one's own will.

Self control

Of course you need self control for tai chi. Self control is a very important part of martial arts generally. With self control you are capable to keep your inner peace. The better you can keep self control, the better martial artist you are.