Heart Position
A grateful heart is aligned with our generous God. A complaining heart is aligned with our flesh nature of entitlement and not acknowledging that we deserve little and yet God provides so much (all). A thankful heart is intertwined with the Fruit of the Spirit (love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, and self-control). A grumbling heart is intertwined with our flesh characteristics (selfishness, bitterness, jealousy, impatience, easily angered, abrasiveness, et al). The position of our heart (our mind) is a reflection on how and who we are intertwined with.
Therefore, do everything without grumbling and complaining (https://www.biblegateway.com/passage/?search=Philippians+2%3A14-15&version=NIV) and be thankful in all things (https://www.biblegateway.com/passage/?search=1+Timothy+4%3A4-5&version=ESV) so that our heart position is intertwined with God’s goodness and greatness (https://www.biblegateway.com/passage/?search=Matthew+6%3A21&version=AMP).