The Hebrew word that is translated blessed can also be translated happy in some instances although in some contexts happy does not fully convey the thought of blessed.  There are passages where correction and trials are termed as blessed but the recipient is not necessarily "happy".  Therefore the word blessed conveys more perfectly a state of well-being with an eye on a better future state.  Those who keep the Lord's commands may not always be the most absolutely "jovial" but we can be blessed in knowing that our ultimate state will be better for having kept the Lord's commands.

Happiness can also be very "situation-driven" but blessedness is dependant upon one thing--the Blesser. We are blessed because God has blessed us.  Doing God's will and seeking Him causes Him to pour out His favor upons us and as a result we are blessed. Just as Balaam could not pronounce a curse over what God has blessed so likewise when we are blessed we shall not be cursed.  Just as blessedness has a future contingency of well-being; cursing also has a future contingency of sorrow. Be blessed!