As @Wormwood already mentioned: you might have bad board layout. This means that it lacked for right colors or you was not able to make a combo. Defense team always strikes back regardless of a board, while you do tile attack by matching.
Also, pay attention to why you lost. Possible root causes:
- Defense team had healer or healers that effectively worked and cured all the defense team while you don’t have a healer and was not able to recover from attacks.
- Defense team had a hero that buffed your team (blind, weakened, decreased your defense or burned) and you was not able to remove those buffs from your team.
- Defense team had a hero that increased there attack strength (Wu Kong for instance).
etc.
Actually, there is a very interesting and useful summary of raid tactics.