Attack wins matches,defense wins championships!

[Tactician]

If your defense is weak you will conceed more goals and you will also score goals.

True. But still, you can decrease the amount of conceded goals by using high pressing.

By the way, defense and attack are equally important, especially if you play in all 3 competitions. The mentality to be used is chosen according to the the situation that will be faced.

Like I have said, the combination of defensive and force counter-attacks seems to work in this game because most teams, irrespective of whether they are stronger than your team or not, will use an attacking mentality. But if you face a good manager or the right tactics were selected by coincidence or other, it may fail, even if his team is weaker than yours.