i would hazard a guess, that is because you don't have the holy Spirit ? if you did you would be an effective witness .. but the thing about being an effective witness is simply .. you need to have witnessed something in order to effectively testify of it .
the other most common cause of not being an effective witness for the lord Jesus is fear and being poorly equipped to do so through many poor and often false doctrines
I try not to guess what gifts people have been given.
Sometimes observation works, but even that gift is rare.
The powers of love and Hope being the greatest gifts of all.
Zechariah 7:9-10
“Thus says the Lord of hosts, Render true judgments, show kindness and mercy to one another, do not oppress the widow, the fatherless, the sojourner, or the poor, and let none of you devise evil against another in your heart.”
1 Peter 4:10
As each has received a gift, use it to serve one another, as good stewards of God's varied grace:
James 1:17
Every good gift and every perfect gift is from above, coming down from the Father of lights with whom there is no variation or shadow due to change.
Ephesians 2:8-9
For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast.
Romans 11:29
For the gifts and the calling of God are irrevocable.
Colossians 3:17
And whatever you do, in word or deed, do everything in the name of the Lord Jesus, giving thanks to God the Father through him.
Romans 12:3-8
For by the grace given to me I say to everyone among you not to think of himself more highly than he ought to think, but to think with sober judgment, each according to the measure of faith that God has assigned. For as in one body we have many members, and the members do not all have the same function, so we, though many, are one body in Christ, and individually members one of another. Having gifts that differ according to the grace given to us, let us use them: if prophecy, in proportion to our faith; if service, in our serving; the one who teaches, in his teaching; ...
2 Corinthians 9:15
Thanks be to God for his inexpressible gift!
Acts 2:38
And Peter said to them, “Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit.
1 Corinthians 12:1-31
Now concerning spiritual gifts, brothers, I do not want you to be uninformed. You know that when you were pagans you were led astray to mute idols, however you were led. Therefore I want you to understand that no one speaking in the Spirit of God ever says “Jesus is accursed!” and no one can say “Jesus is Lord” except in the Holy Spirit. Now there are varieties of gifts, but the same Spirit; and there are varieties of service, but the same Lord; ...
Romans 15:13
May the God of hope fill you with all joy and peace in believing, so that by the power of the Holy Spirit you may abound in hope.