Sir Clive Woodward has named a strong side to play Bay of Plenty as they attempt to hit the ground running.
"Every game we play here in New Zealand we will be tested," O'Sullivan said.
"That makes a Lions tour unique and if we don't go into every game with that mentality we will get turned over. That starts in Rotorua where Bay of Plenty will try and throw the kitchen sink at us.
"We have got to get our heads around that very quickly. That will make us a better team. We will get to the Test side knowing all the players have been put through the mill and we know what we are picking from.
"It gives you the best opportunity to pick your strongest side to win the series. That is why we are playing all these tough games."