More or less everyone have moments when we feel a bit down on ourselves for various reasons. When you are feeling real down and have negative thoughts about yourself and your ability, well that is not a good place to be in. But it is a normal thing to get into that mindset sometimes, then what is best is to try to get out of that mindset as fast as possible. You may need support by a good friend to change your way of thinking about yourself if you feel really down. But that is not a weakness, we all need support from friends from time to time.
While we are feel down and out that just takes energy from us, so try to stay positive and think about all the things you are good at, instead of just focusing on your limitations. It is not always that easy to realize that we really have a lot of good sides and skills when feeling down,but try to realize your good sides. Negative thinking will not take you anywhere where you want to be, it just drains you on energy... Feeling down on yourself doesn't have to be connected to struggling in marketing, but if you are struggling then here is free training... And it is totally okay to feel down as long as you keep coming back up.
If you needed inspiration and motivation,then by reading my pres release, I hope you received some of that.
All the best,