This negative self talk can come from many different things. Mine was from several different sources. First my dad, no matter what I did it was never good enough. Several things that I would do for school he would add his finishing touches to. So, "I can't do anything right." Secondly, after I had a major my orthopedic told that I couldn't do several things because he had to fuse my ankle. Now add, "I can't because I'm broken." As you can see we start building the negative self talk on top off each other and soon it shuts us down from doing anything.
We also start internalizing and believing the negative self talk is true. Next thing that we do is start interpreting others actions and words according to our negative self talk and make it out to be against us even when it has nothing to do with us. We then withdraw and eventually spiral into discouragement even depression.
The negative self talk gets so loud that we can't hear what God is saying to us. If we do hear Him we use the negative self talk as to why we can't do what He is asking us to do.
For a long time I would listen to the negative self talk and it kept me from doing what God had asked me to do. Tried using some of the excuses that Moses used. Must admit if they didn't work for him want made me think that they would work for me.
One of the best quotes on overcoming negative self talk came from Chuck Norris, "A lot of times people look at the negative side of what they feel they can't do. I always look on the positive side of what I can do." That is what God was doing with Moses. Every time Moses came up with an excuse as to why not him, God showed why him. God showed Moses long before Paul wrote it, "I can do all things through Christ who strengthens me." (Philippians 4:13 NKJV)
In high school, back in the 80's, I was involved in a youth choir. One of the songs that we sang was "Moses" by Ken Medema. I found "Moses" on You Tube preformed by Ken. At the very end of the song is the clue to the negative self talk, "Give it up. Let it go. Throw it down."