Why do they say they will do something and then do the total opposite?

I can't count the number of times H has said he's going to do something right now and then does something completely opposite. What is it in their brain that makes them say things when it seems like they have no intention of doing it? Just this past weekend he tells me at about 2PM after he just got done with about 2 hours of video gaming "Let me take a shower and then we'll go run errands". What does he do 20 seconds after telling me that? He grabs his guitar and sits down and plays that for about 30 minutes and THEN goes to take a shower! Then later on that night he tells me "Tomorrow why don't we head downtown and do some stuff?" I say "That sounds great" because I'm up for anything to get me out of the house. The next day at 2PM he is in front of his computer in his pajamas and has not said one word about going anywhere. I bring it up to him and he goes 'Nah. I'm pretty comfortable right here". He tells me he's going to go online right now and send me his share of money for the bills. 5 minutes later I walk into the computer room and he's playing his video game. I say "Did you send me the money?" He goes "No. I'm going to wait until my accounts stabilize and I'll send you some in a couple of days." He tells me he's going to go lay down for a nap, yet he goes into the computer room to play his game and never does nap. He does this with other people too. He gets all excited about getting his motorcycle on the track and tells this one guy he'll do a certain weekend with him and gets him all hyped up about it. Then tells me a few hours later "I really don't want to do that weekend. It will be so crowded." Yet he doesn't tell the guy that and lets him believe he'll be there. Same about fixing a guy's motorcycle. He worked on a bike for a friend of a guy he works with. This guy told his friend and he contacted H. H says "Sure I"ll take a look at it". This guy then texts H saying "Great. I'll be home after 2PM both Sat and Sun and will be available then." H then complains to me that he doesn't want to fix this guy's bike but doesn't tell him that. The guy is obviously excited to get it looked at and texts H saying "I'm home now so anytime is good." H ignores the text. The guy texts again at 2 on Sun. "I'm home" and H ignores the text.

I mean I just don't get why he says all this stuff when it seems like he's just saying it to say it and has no intention of following through.