You might not know who the Psalmist is referring to in Psalm 110 upon first reading it. But if you check out some cross references it becomes clear he is speaking of Jesus Christ, the Lord. This is how you discover that the Bible is its own best commentary.
Verse 1 is referred to by Jesus in Matthew 22:41-46 and by Peter in Acts
Other references based on this Psalm could be found, but these are sufficient to affirm that David is here identifying a human being whom he calls his Lord. That one is none other than Jesus Christ. He will have the final word, so it would be wise, like David in this Psalm, to affirm Jesus Christ as your Lord and God by faith, surrender to His control, and follow Him wherever He might lead you. Then it can be said of you, “You can’t lose for winning!”