In an interview with the Evening Standard, Lewis said: I needed to find out for myself whether I can lead a whole business.
Some people think that is crazy given some of the jobs I have done but actually I dont think you know whether you can truly lead a business until you sit in that seat.
Lewis was parachuted into the Tesco top job yesterday, a month earlier than planned, replacing former chief exec Phil Clarke.
The appointment follows a varied career at consumer good giant Unilever, where he specialised in marketing and also held MD roles around the world, but admits that he has never ran a shop in his life.
I am wonderfully nave about some of the stuff that is going to come but that is fine, it has served me well up to now,” he said
I will do what I have to do tomorrow in the same way that I did things yesterday.
Despite this, he thinks he can bring a useful new perspective to the role.
He said: Phil Clarke is a great retailer. The issue for Tesco is, is that what they need now” Because great retailing in that seat hasnt been the thing that has worked, so they do need a fresh perspective.