Read on Twitter
Mentoring(or "why has this player's Determination changed!?")
#FM20
- Young players will be influenced naturally by those more senior around them
- This influence can shift the player's Personality and Player Traits towards that of the player they were influenced by
- This shift happens between players in the same squad
- It is more likely to occur between players in the same Social Group and/or Training Unit
This happens regardless of Mentoring 
- Mentoring allows you to bias it towards a specific group of players
- Mentoring can only occur between players in the same squad, as they need to be spending time together on and off the pitch
- The players with a higher influence in the group will be more likely to mentor those with a lower influence
Factors that impact a player's estimated influence include...
Captain/Vice-CaptainHierarchy
Age
Appearances
Time at Club
Reputation
- Players are less likely to be influenced by others after the age of 24
Player Traits can only be passed on between appropriate players. For example, a GK cannot learn 'Shoots With Power' from a ST
Determination 
Ambition and 
Professionalism are affected by MentoringFor more on those three attributes, see - https://twitter.com/SebWassell/status/1261699250460798981
