Tottenham boss, Jose Mourinho has hailed former Arsenal manager as the last of his kind, adding that it is impossible for coaches to match the 20-year dynasties that Alex Ferguson and Arsene Wenger achieved.
He noted that Premier League bosses are now forced to "fight for our job every day."
Mourinho was appointed Tottenham head coach last week after Mauricio Pochettino was sacked just six months on from guiding Spurs to the Champions League final.
Another high-profile departure followed on Friday as Unai Emery, Wenger's replacement, lost his job at Arsenal after 18 months at the helm.
Manchester United have similarly struggled to fill the void left by Ferguson, who reigned for fully 27 years at Old Trafford.
Mourinho acknowledged that job security rarely lasts longer than a day now at top clubs.
"Twenty years in a club? I don't think it's possible," he told reporters.
"Modern life, new technologies, social media - I think everything has an influence, even people's mentality, faster relations, getting tired easily, so many things that are changing.
"Not [just] football but [these things] are changing the world and the perception of things that I think Wenger was the last 'man/one'. It's a bad thing for us.
"We have to adapt and we have to try to prove that we are the man for the job. We have to fight for our job every day.
"I think the times where people know the job is going to be mine for X amount of years [are gone]. You have to fight for your job every day. Not just with the football results but with everything you do in the club.
"I think it's normal. It happens in society in so many areas. I can imagine even yourself in your newspaper and your radio you have to not just sleep on what you did previously.
"I think you have to show every day you have that you are the guy for the job. I think it's just life."
But Portuguese said he does not go into new jobs worrying about how long his tenure will last.
"I don't think about that," he said, adding "I think about trying to show I am the man for the job every day."