I don't measure a model as a failure when things don't go right with glues, paint work or other issues, i treat those as learning mistakes to which i plant more effort into resolving before doing my next.
I wouldn't down grade your efforts with some models regarding them as failures, look at them as the best of your ability's, not everyone is a highly skilled craftsman able to produce museum quality work. So by saying the model is a failure your only belittling your own efforts, in turn making your next project all that more daunting and the final result will be just as 'bad'.
They say ''you are your own worst critic'' and that's true but its all part of the learning curve, when i first started modeling i made all sorts of mistakes some of which looking back now i would blatantly lie i never built it!
That said if not for those mistakes i wouldn't have learnt anything to improve for the next, there is always a transition as you improve each model will always be better then your last and that's where you should be proud of yourself rather then being negative towards an imperfect model.
I'm a big one for not finishing projects in reasonable time ( i was up to 11 outstanding last year now i'm down to 9, with my oldest project being some 7 years in the process from a model that's already 60 years old !) ,some through lack of effort some from lack of enthusiasm is mostly the case on particular projects (those tend to be the ones that have fought to be built) , but they all get done slowly, i'm catching up now! to which i can only say life happens.
So in simple terms don't look at your models as failures be proud of your achievements to date and don't worry what everyone else thinks, I couldn't give a flying monkeys what anyone thinks of my builds, i had fun building them and thats ALL that matters!