Why does something always go wrong?

No matter what the build no matter how careful or patient I am something always goes wrong.  Sometimes its not to bad but sometimes it goes so wrong that there is no other option but to start again and why does it always goes wrong when it seems to be going so well? Take for example the model below.......

This model was so close to being completed, it had fought me all the way and I was looking forward to it being completed.  So the paint was on, which had come out really well the gloss was down and the decals were on  which again had gone really well.  Just the panel line wash to go and the matte coat and it would be done! I used the usual oil wash which at first seamed to go really well, then disaster.  For some reason on the white the oil wash seemed to stick leaving large parts of the white around the nose and tail a dirty grey/black.  Usually at this point the anger builds up and the model  has a little flight before a crash landing , but this time the model went back on the shelf of shame.