Sanctification comes at a cost. Sanctification costs the Christian their flesh.
For example, if a Christian is naturally very impatient in the flesh, the Lord may allow many trials to come that require the Christian to exercise their patience. Although difficult, the Lord always extends His grace to overcome the trials.
Trees must be pruned to grow better and stronger.
In the same way, the parts of a Christian's lifestyle, actions and thoughts that is worldly or that succumbs to the flesh, will be pruned by the sanctifying work of the Spirit. These parts will wither and die over time.
If one earnestly seeks to be sanctified, they must understand and be prepared that sanctification holds hands with sacrifice.