I draw your attention to this post as Pastor Schlueter doesn't speak of pietism in vagueness, but goes so far as to help us define it.
Pietism has at its heart the notion that the individual is and can be better than they are. Pietism promotes a self-delusion of personal righteousness that one must hold on to at all costs. Because pietism is built on your moral improvement you have to hold out for your own goodness, you have to pretend on the surface that you are "pulling it off", that you are living the Christian life, that you are an example for everyone else to follow. As a result, pietism forces us to overlook the sin that lurks within.
Speaking for myself, I am a great poseur. It's easy to make like I am pulling it off, like I am holier than this guy or that gal because at least I have never done "that." And THAT is way worse than anything I have ever done.
It is important to note that there is "piety" and then there is "Pietism."
Piety shows itself in our personal devotional lives in the form of reading the Bible, singing hymns together as a family, saying a prayer before and after a meal, etc.
Pietism takes our everyday piety to the extreme, and turns the focus of our piety on ourselves instead of on Jesus.
A good hymn that speaks of appropriate piety is "Let Us Ever Walk With Jesus."
Let us ever walk with Jesus,
Follow His example pure,
Flee the world, which would deceive us
And to sin our souls allure.
Ever in His footsteps treading,
Body here, yet soul above,
Full of faith and hope and love,
Let us do the Father's bidding.
Faithful Lord, abide with me;
Savior, lead, I follow Thee.
Let us suffer here with Jesus,
To His image, e'er conform;
Heaven's glory soon will please us,
Sunshine follow on the storm.
Though we sow in tears of sorrow,
We shall reap with heavenly joy;
And the fears that now annoy
Shall be laughter on the morrow.
Christ, I suffer here with Thee;
There, oh, share Thy joy with me!
Let us also die with Jesus.
His death from the second death,
From our soul's destruction, frees us,
Quickens us with life's glad breath.
Let us mortify, while living,
Flesh and blood and die to sin;
And the grave that shuts us in
Shall but prove the gate to heaven.
Jesus, here I die to Thee
There to live eternally.
Let us gladly live with Jesus;
Since He's risen from the dead,
Death and grave must soon release us.
Jesus, Thou art now our Head,
We are truly Thine own members;
Where Thou livest, there live we.
Take and own us constantly,
Faithful Friend, as Thy dear brethren.
Jesus, here I live to Thee,
Also there eternally.