Enjoying the writing! When the work is going well, you really do get a buzz out of it!
Enjoying other writers’ work more. You do appreciate the effort more when you have a go at story telling yourself!
When you want to write but the sadnesses of life get in the way. (I try to write anything during these times. Something good may come from it later).
When your head is buzzing with ideas, which sounds an odd thing to list as a frustration, but it can mean being stymied by the old question as to which you follow up first!
When your head isn’t buzzing with ideas as that is more obviously a worry!