'Happen' in the Bible

out of the same mouth doth come forth blessing and cursing; it doth not need, my brethren, these things so to happen;

Yet you do not know [the least thing] about what may happen in your life tomorrow. [What is secure in your life?] You are merely a vapor [like a puff of smoke or a wisp of steam from a cooking pot] that is visible for a little while and then vanishes [into thin air].