Agent of Thwart

Reach my hand intend to
 Raise this cup of drink to
 My mouth but it spills down
 Poor miscalculation
 Failing to account the
 External influence
 That blasted agent of thwart
 No answer agent of thwart
 Disaster agent of thwart
 Supplant the agent of thwart
 Go faster agent of thwart
 Your password agent of thwart
 To master agent of thwart
 Plan to see what will be
 Practice flow for easy
 Modelling of forces
 So I add my causes
 Fill the drinking glass up
 Thinking like a grown up
 Dare to act should imply
 There's no need to ask why
 See effects of where you reach
 Be true to how you speak
 It makes the outside real
 That blasted agent of thwart
 No answer agent of thwart
 Disaster agent of thwart
 Supplant the agent of thwart
 Go faster agent of thwart
 Your password agent of thwart
 To master agent of thwart