Hi - you've only just joined the forum and so you probably don't realise you've stepped into a minefield. Actually - you've got both feet in two separate minefields!
Before the first one goes up think about this - What do you mean by logical? Do you think it's not logical to choose to try one and then the other of the only two possible candidates for a cell?
As far as the second one goes - I bet there are puzzles out there that you cannot solve except by choosing a candidate and trying it to see if it works. For myself, there are these puzzles also, but there are fewer now that I've learnt some techniques. I cannot speak for the others but quite a lot of them are very brainy and so there might be one or two who never have to do this.
PS : This has been posted in the wrong place in this forum - read
this .