One way to know whether a behavior is self-defeating is to examine it in the context of your long-term goals or desires and determine whether it is consistent with them.
Take the case of excessive reassurance-seeking. It occurs when people experience self-doubt and desire strong relationships but, in order to feel more confident and connected to others, ask friends and family for signs of love and acceptance ("You still like me, right?"). There's nothing wrong with asking for reassurance now and then, and most people are happy to provide it.
But many people go overboard and ask over and over again. They wind up pushing people away or aggravating them, and the reassurance stops, which creates even more self-doubt.
Excessive reassurance-seeking can potentially cause depression and relationship problems, and it often works in a cyclic fashion: Once doubt sets in, people seek more reassurance more often, alienating others, compounding relationship problems, and exacerbating depression.
People also self-sabotage due to mistaken beliefs about a behavior. It's common knowledge that when you're angry you should scream into a pillow or punch a punching bag and "get the emotion out," right? But studies find that venting anger actually makes people angrier!
Hitting a punching bag makes you more likely to scream at or even attack someone. As researcher Brad Bushman puts it, venting anger is like "using gasoline to put out a fire-it only feeds the flame."
Connecting a behavior to problematic consequences does not guarantee the ability to disengage from the behavior. Think of self-sabotage as a pattern developed over time, rather than one instance here or there.
Are you not getting updated headshots? Are you waiting until the day of to prep for a casting? Are you not testing to build your book as a model?
Which behaviors do you practice that aren't lining up with your long term goals as a talent?