How to convince someone that I'm really committing?

[Isaac k]

How can I promise a boss that I'm really committing to a job after in the past I took jobs from the same boss and in my heart I didn't really commit and I didn't do my work good?

[RobertZ]

You say that in the past you did not commit in your heart—but in the past, did you make a promise to the boss and break that promise? Or, did you simply not meet the boss’ expectations in the past? 
 

If you simply did not meet expectations, you could try acknowledging those mistakes and explain that you are resolved not repeat those mistakes, but improve. If you made promises in the past and didn’t keep them then talk is cheap. You might have to earn some trust back—maybe a probationary period or service? 

[Thought Art]

Show them your results 

[Tim R]

Let your work speak for itself. 

[Egzoset]

Simple:  Just learn to master mind control!!

 

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