"It was hard when I didn't make the initial squad because it is everyone's ambition. To now be selected is a massive honour," Best told the Ulster Rugby website.
"To finally be selected makes playing professional rugby worthwhile. All the lows that you get and the knocks and bumps, it more than makes up for them and for a few weeks ago when I thought that the chance had gone.
"There will be 37 players getting on a plane to Hong Kong aiming to make the Test squad and I am no different. I am as ambitious as everyone else. To be on the tour is unbelievable but you have to go there and play your best rugby, put your hand up and see where that takes you."
Lions head coach Warren Gatland revealed that the selection debate over the hooking positions in his squad was by far the longest and toughest of any he had with his selectors.
"Rory was very, very unlucky to miss out. One man's disappointment is another man's fortune and I am sure he will come in and do a great job," said Gatland.
"When we picked the squad it was very, very tough. The decision on the hookers was by far the longest debate we had.
"In previous tours, when players have had that chance they have come in and made the most of it. He has the chance to do that."