If you possess only this one thing, you have everything you need to be grateful. The one thing that provides you what you need most of all is unconditional love from one person. Unconditional love from more than one person creates an overwhelming abundance and every reason on Earth to be grateful beyond any measure.
Not only do you have the capacity to accept and appreciate unconditional love, but you also have the power to provide it to others, giving them the greatest and most powerful gift possible, one for which there is no substitute, including money or material things, success as it is commonly measured, or anything else that we mistakenly perceive as being valuable.
You may already possess many things for which you give thanks, but the one that matters most is the unconditional love that means you matter most to one other person.