The thing is any transfer with even the worst motivations can work. If things fail it's just a personal failure of someone in the chain of command. 'Failed transfer' is just a broad escape gate term when something goes wrong tied specifically to a stint in one club, but transfer almost always applies to the operation rather than the player, which is nonsense as in many cases the buy will make every bit of sense. For a long time I suggested it's just about finding the person to call out over lack of success with a player, who at top level almost always has talent or in its absence other redeeming qualities which made the sporting directorate go for him. Shouting flop doesn't impress anybody. By applying flat criteria Griezmann and Coutinho have started as failures as both signed with poor motivations, after a lengthy bad PR saga, for positions that are occupied/unsuited for them/don't exist. Except it's not even close to fair to players themselves who were both great in previous teams, club or NT. Had nothing to do with their football.
Hazard doesn't carry even 10% of the blame and if any, it's only for that period of "oh yea, I'm finally in Madrid, let's have a beer bash" after which he was a model professional for all anyone outside the club knows.
There's also the problem of people tendency to judge prematurely. Most reasonable people will be happy to call it a day when a player you've invested in for the long-term is average/patchy/inconsistent etc after ~7000 mins on the pitch (roughly 2 seasons). It's what getting a chance really means for a younger player.
And then you still have those arguing appearance numbers are worth anything without consideration of minutes played and players must perform in their 5-15 minute episode irrespective of whether the coach puts him in a position to succeed, familiarity with the team, the country, all the rest of it. Just impose yourself on the game. What bollocks. Utter lunacy.
First criterion is that player takes things seriously in a new place. Second is that manager has to play them. If not, either coaches lose confidence in you doing the job, or you lose confidence in them for noticing your job. And then dude will try to climb walls and go back to where he knew he felt comfortable to regain the lost confidence. Normal course of events.