The knowledge that Paul is talking about is only possible by grace. It is a revelation rather than something we work ourselves to. This grace loves us even when we are unlovable: as Paul says in Titus 3, we were hated and hated one another when the kindness and love of God appeared. If this love is by grace, then any knowledge that we have about it can only be by the same grace.
Having lived through it, I know now it was God’s grace that kept me pressing forward to the many blessings I have today. That doesn’t mean God has granted me every wish I’ve ever asked for but it does mean that he has helped me live free of needing every wish in order to find peace and joy in life.