'For I am yours... and you are mine' (see Isaiah 43:1). Yes, it may seem a bit like a greeting-card clich. We may know in our heads that we belong to Jesus, but knowing in our hearts that we belong to him can be harder to accept. What does 'belonging to Jesus' mean, anyway? What difference does it make to how our lives look?
The real sense of value that comes from knowing we're children of God doesn't come from the nice things he gives us, or in fact any 'thing' that can disappear at any time. God's declaration that we are his, and that we are significant because of this, isn't him saying, 'I shall give you, my child, anything you want to do or desire.' God's acceptance is a lasting significance that won't be outdated in six months: 'I have called you by name; now you belong to me. When you cross deep rivers, I will be with you, and you won't drown. When you walk through fire, you won't be burned...I am the Lord, your God...To me, you are very dear, and I love you' (Isaiah 43:1-4 CEV).
We are precious. Not for what we have, or for what we've done - just for us. When our sense of significance is based on an inside job through Jesus, rather than on external things, nothing can touch it.
So what now? You are significant because you belong to God. Tell yourself this regularly, maybe even write it somewhere to serve as a reminder. Allow nothing or no one to convince you of anything else.