November is the month dedicated to the Holy Souls in Purgatory. These souls suffer because even though they know they will eventually be in God's presence for eternity, they are not there yet. We as the Church Militant can do much to shorten their time in this place of purgation. We can offer the Holy Sacrifice of the Mass for them, and we can remember them, especially those of our family and friends, in our daily prayers.
St Therese of Liseux believed that with enough love and trust in God, Purgatory could be avoided. She believed to see Purgatory as the norm for souls rather than the exception was a grave error on our parts.
Her teaching on this is not dogma; we are not obliged to believe it. However, this great saint is a Doctor of the Church, and there is much truth in what she says. You can read what the Little Flower has to say about avoiding Purgatory here.
All that being said, I am still grateful that God gives us this last chance, so to speak, to become totally clean and purified so that we may enter His Kingdom to love and praise Him forever.
Here is what the Catechism of the Catholic Church says on the teaching of Purgatory: