The former England captain, who stood down from the job on Monday after leading them for a record 59 Tests, conceded England’s progress had plateaued as he spoke in depth at Lord’s about his decision.
“The last year, we played some good cricket but we lost eight games and we have kind of stagnated if we are being brutally honest as a team,” said Cook.
“There is a lot of work that needed to be done I felt and I just didn’t have that energy to do that.”
Asked whether he felt responsible for that stagnation, Cook said: “One hundred per cent, yes. That’s part of the parcel of being captain. You are responsible and that is never a great feeling when you lose too many games.
“Sides need a fresh boost of energy and probably new ideas and new thoughts to get the best out of them.
“I tried everything and I feel like I have done my bit on that side. Ultimately that is what helped to make the final decision for me.”
Alastair Cook steps down as England Test captain
Mon, February 6, 2017
Alastair Cook has stepped down as England Test captain
1 of 6
Alastair Cook has stepped down from his role as England Test captain
Alastair Cook believed England had stagnated under his leadership
Cook, 32, who looked contented and refreshed after five weeks at home, named the 2015 Ashes series as his personal highlight of four years in the job, a series England edged 3-2 despite being given little chance beforehand.
Yet the reality since then has been of the odd flash of brilliance amid declining fortunes with just seven wins, four draws and 10 defeats in 21 Tests since that summer, culminating in losing five out of their seven matches against Bangladesh and India this winter.
It has been a run which Cook said left him drained.
“I knew when I got on that plane home from India that it was very unlikely that I would ever captain England again. I just had my fill of it in one sense,” he said.
“There have been certain times throughout my four or five years in the job when I’ve been to the well and dug pretty deep and when I looked in that mirror, I felt it was time.”
Alastair Cook named the 2015 Ashes triumph as his finest moment as captain
One of those tough times was Kevin Pietersen’s controversial dismissal from the England team in 2014, and Cook said: “It was obviously a big part of my captaincy. I felt like it wasn’t handled particularly well from the ECB.
“I was the lightning rod for it. Every person thought it was my decision and I bore the brunt of that, unfairly in my personal opinion.
“As much power as you have as the England captain, you don’t get the ultimate decision on that thing. I was part of the decision making - as six or seven others were - but I didn’t have the final trigger.
“I felt a little bit let down by the ECB in that one period where they left me out to dry a little bit.”
But Cook still enjoyed the majority of his time at the helm did not take the decision to step down lightly, adding: “It was sad in one way, because I’ve loved the honour and prestige of all of it. I’ve been leading some great men and had some great moments as England captain.
“But I do think it’s the right time for me and for the team.
Alastair Cook expressed his regret at the sacking of Kevin Pietersen
“It is a job that you need to do at 100 per cent, being right on it all the time with ideas running through your brains and pushing England forwards. The thought of doing that was not exciting.
“I could have done it at 90 or 95 per cent but that’s not enough for England captain.”
Joe Root, 26, is red hot favourite to be announced as Cook’s successor, most likely next week after the formal process of identifying the 80th England Test skipper has been completed.
And if, as expected the Yorkshireman succeeds the opener, Cook hopes to be able to help out with the odd piece of advice as they move towards the Ashes in Australia next winter.
“The next guy will have tough moments as well but if I had one piece of advice it is that you don’t always have to do it your way,” said Cook. “There are a lot of people out there who watch a lot of cricket and know more than you do or anyone does.
Joe Root looks set to succeed Alastair Cook as England captain
“Use that advice and be open to it. Ultimately you have to make that or those decisions out there yourself but take as much advice as you can because a lot of people want you to do well.”
And despite leading England’s runs scoring and Test century charts Cook has unfulfilled ambitions at the highest level which he hopes he will get the chance to achieve.
“I look forward now to the next part of my career now,” he said. “I look forward to supporting the new guy as best I can and I look forward to hopefully scoring some runs and being part of England’s success.
“I hope I can help the next captain with whatever he needs and drive England forward and I can’t see, for me, it being an issue being led by someone else. I hope I can be part of it and I’m really looking forward to the next stage.”