Even the most successful authors/artists get this. It seems to be part of the creative process. The best thing you can do is try not to beat yourself up about it, take a step back, breathe, read through some positive comments on older stories, etc.
For a stalled WIP though, try some of these:
-If you are stuck at a particular scene/section, try writing events past that section that you can get momentum on, then come back and stitch the parts together after. Sometimes it's easier to proceed if you know where you need to go.
-Set it entirely aside for a few days, go for a walk, get outside, let yourself ignore it, then come back fresh after.
-Try going back to an earlier scene and doing a rough second version of it from another character's perspective
-write a journal entry for one or more of your primary characters about what they have experienced in the story so far and what they think and feel about it
-freewrite anything, just write whatever comes into your head, get it down on paper or in a text file or if you're brave, something like Write or Die (the web app is here: http://oldandbusted.drwicked.com/#Web+App ). Sometimes it helps to just get words out, and sometimes you can turn it into free association brainstorming about plot points or character developments
-write a completely unrelated drabble or ficlet or poem, and post it.
Re: Dealing with insecurity
For a stalled WIP though, try some of these:
-If you are stuck at a particular scene/section, try writing events past that section that you can get momentum on, then come back and stitch the parts together after. Sometimes it's easier to proceed if you know where you need to go.
-Set it entirely aside for a few days, go for a walk, get outside, let yourself ignore it, then come back fresh after.
-Try going back to an earlier scene and doing a rough second version of it from another character's perspective
-write a journal entry for one or more of your primary characters about what they have experienced in the story so far and what they think and feel about it
-freewrite anything, just write whatever comes into your head, get it down on paper or in a text file or if you're brave, something like Write or Die (the web app is here: http://oldandbusted.drwicked.com/#Web+App ). Sometimes it helps to just get words out, and sometimes you can turn it into free association brainstorming about plot points or character developments
-write a completely unrelated drabble or ficlet or poem, and post it.
Hope that helps.