question about a move analysis sair it was a mistake

Hi guys

Im rookie in chess, this is my fisrt post ever. I have a doubt about a move lichess analysis considers a mistake, but i dont understand why. I dont even think the suggestion is any better

This is the position (im white)

http://pt.lichess.org/bUabrhPD/white#14

I played:

8.e5

My aim was a8 black rook.

My pawn was not protected, i hoped black queen to capture it 8 ... Qxe5

Response 9. Bg2xc6+, black defends king, and then 10 Bc6xa8.

As u can see in game, black wasnt fooled, he played 8 ... bc8b7

then i responded 9.Bc2f4, covering e5 pawn and manacing black queen.

However, Lichess thinks 8.e5 move was a mistake and that i should have played: 8. exf5

8. exf5, Bc8xf5 9. Bc2f4, Qc7c8 ....

I understand the engine have a diferent logic, but i dont cant see why 8.e5 move could be considered a mistake.

Is there something im missing?

Ps: sorry if didnt made myself clear. New in chess and not english not native language.

"Mistake" is one level below blunder. You should ALWAYS be able to figure out a blunder, albeit perhaps with full assistance from an engine. Full assistance means the ability to explore alternative lines, which you cant do if you have only Lichess for analysis. Just get one of the good free programs for your phone, Smallfish for iphone or Droidfish for android. You wont always be able to figure out mistakes even if you use an engine.

In this case, as I see it, you played hope chess, hoping your opponent would make a terrible blunder. If he doesnt take the pawn, what does e5 really do? Its not a terrible move per se, it does make developing the black knight harder and grab some space. However, you already have a development lead, and if you open that diagonal for your dark square bishop with pxp, your going to develop it for free on a great diagonal -- free because his queen has to move. You get further ahead in development and have wonderful open diagonals to work with. Your two bishops then have massive scope, raking the queenside, black has an isolated pawn and no development. Nd4 becomes a threat.

Take away: it is usually good to open up the position when your ahead in development, and when your bishops can use the open space effectively.