Actually one of the things that affect most clubs is lack of planning, though in as much as they would already have all the kind of players they needed but planning ahead of time is always one of the most important thing because majority of clubs has been going through a lot because of the inability to have put things in place, so actually just like you said since Mohammed Salah is the most valuable and the most experienced player in Liverpool what the team management supposed to have been doing is to be striving for a good player that would replace Mohammed Salah because already the club management knows that Mohammed Salah will not play for Liverpool till he retired so working on those things now should be there number one priority because if Mohammed Salah leaves the club without any replacement Liverpool will seriously be affected before they would get use to it.
Lack of planning is out of any coach, the problem with some of them is incompetency for the game and lack of strategy. You know Premier League is one of the watch league in the world and been available as one of the coach automatically makes you popular, makes you available for other opportunities. What some of them want is fame yet they lack the qualities to be there, you want to represent a big club yet you don't have what it take to help them win the league.
Look at Lampard for example, he was a good players and was well respect, had a good time in Chelsea but loo at his career since he signed up been a manager, he has never achieved anything serious in his career, this is to say not all great players make good coach and not all good coaches were once a player in their life time. There are some of them that never play for any club and yet they are good because to coach is another talent on it own.