Many times "self-deliverance" will work. There are also many times it doesn't. Here is a list of reasons for why it doesn't work.
REASONS FOR FAILED DELIVERANCE
1) LACK OF REPENTANCE
A close review of the Requirements for Deliverance reveals that there must not be the slightest connection to SIN. The reason being, a believer is already blood bought and has yet chosen sin over and over without hesitation and repentance. God requires total repentance (not holding back onto that little "secret sin"). Brethren, I don't know when someone says they have repented from ALL sin whether they have or not; but GOD KNOWS. The one seeking Deliverance must repent of ALL SIN.
2) LACK OF DESPERATION (TRUE DESIRE)
Again, this is something that can only be discerned by God/the Holy Spirit. So, if it appears as though one has repented of all sin and truly wants Deliverance, God knows and will not accept less than what is required to expel the evil spirit(s) that have gained LEGAL ENTRANCE because of A CONSCIOUS CHOICE TO SIN AND TO CONTINUE IN SIN.
3) WRONG MOTIVES (JAMES 4:3)
Again, something that can only be discerned by God.
4) SELF-CENTEREDNESS (DESIRE FOR ATTENTION)
Requirements for Deliverance clearly state that one must be humbled before the Lord. If you're not, God knows.
5) FAILURE TO BREAK WITH OCCULT (haven't disposed of all occult objects)
If you have any objects still in your residence that are connected in any way with the occult, you will have to get rid of them. Our God is a jealous God: Exodus 34:14-17 (KJV) “For thou shalt worship no other god: for the Lord, whose name is Jealous, is a jealous God: 15 Lest thou make a covenant with the inhabitants of the land, and they go a whoring after their gods, and do sacrifice unto their gods, and one call thee, and thou eat of his sacrifice; 16 And thou take of their daughters unto thy sons, and their daughters go a whoring after their gods, and make thy sons go a whoring after their gods. 17 Thou shalt make thee no molten gods.”
6) FAILURE TO SEVER EVIL SOULISH (SOUL TIE) RELATIONSHIPS
If there are unholy soul ties (friendships or even romantic connections that are not Godly), the one seeking Deliverance must break ALL those connections. Breaking does not mean returning to them.
7) UNDER A CURSE – MUST BE BROKEN
If you are under a Familiar (Generational) curse, because of the sins of your mothers and fathers, etc., that curse must be broken.
8) FAILURE TO CONFESS A SPECIFIC SIN (i.e. abortion is murder)
Referring back again to Requirements for Deliverance, you must be open and honest before God. If you've had an abortion (for example) when you're confessing that sin, asking God to forgive you for your sin (in general terms) isn't going to "cut it." God knows what you did regardless, so trying to 'pretty it up' before God doesn't work. Be honest and humble before the Father.
9) NOT SEPARATED BY WATER BAPTISM
The Israelites were delivered out of Egypt “by the water of the Red Sea,” which is a "type" of baptism). It was the water that prevented the Egyptians from following and conquering them. “If a person isn’t willing to be water baptized, they don’t qualify to stay free.” -- Derek Prince
10) PART OF LARGER BATTLE REQUIRING CORPORATE ACTION