I think this is often overlooked. The way we play leaves us open at the back so often, like you said, the opponent inevitably gets chances. With the importance of confidence in the system Martinez plays, softly conceding goals as we did last year took the wind out of the sails of the side and we often conceded more and more. The goals compounded themselves and that's why we saw stupid defeats with turgid football. Palace at home last season was a prime example. We go one-nil up, cruising, playing some really aesthetically pleasing football. A simple ball isn't dealt with by Stones, Howard comes crashing in, Palace equalize, and we collapse. In 13/14, we simply didn't concede too many of these soft goals. We won games with Howard almost always having that one save, the save he didn't make last year near often enough. I felt like we would concede every time the opponent had an effort on net last season, and I think the side felt that way as well.
When the goalkeeper plays well, it bolsters the whole side, it seems as if the confidence in the team radiates out from the goal. The defenders are more sure both with the ball and when defending it, the midfielders are more willing to make the risky pass, and Lukaku benefits mightily from the midfielders feeding him with greater boldness. The goalkeeper has to inspire confidence in the side, and that's why Howard has to be replaced sooner rather than later. A consistently good keeper will transform this side, enabling us to maintain great moments of form, as we did in 13/14.