Behaviour is said to be self-sabotaging when it creates problems and interferes with your goals. Self-sabotaging behaviours include things such as procrastination, reliance on alcohol and stimulants, negative self-talk such as "I am not good enough", spending your time talking rather than doing and not investing or spending time on yourself.
In simple terms it is like a split in your personality with half of you wanting to succeed and move onto other things whereas the other half of you would rather you stayed in your comfort zone where it's safe.