Passage
Thou art not afraid of fear by night, Of arrow that flieth by day,
Thou art not afraid of fear by night, Of arrow that flieth by day,
Psalms 91:3 For He delivereth thee from the snare of a fowler, From a calamitous pestilence.
Psalms 91:4 With His pinion He covereth thee over, And under His wings thou dost trust, A shield and buckler <FI>is<Fi> His truth.
Psalms 91:5 Thou art not afraid of fear by night, Of arrow that flieth by day,
Psalms 91:6 Of pestilence in thick darkness that walketh, Of destruction that destroyeth at noon,
Psalms 91:7 There fall at thy side a thousand, And a myriad at thy right hand, Unto thee it cometh not nigh.
The verse centers on "thou", "afraid", "fear", "night", "arrow", and "flieth". It is saying that the verse draws attention to "thou" and "afraid", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 4's "With His pinion He covereth thee over..." into verse 6's "Of pestilence in thick darkness that walketh...", so "thou" and "afraid" belong inside that flow. In Psalms context, the local focus is worship, trust, the LORD's kingship, and covenant mercy.
A plain takeaway is to answer the verse's own emphasis on "thou" and "afraid" with trust shaped by these words, not by a vague optimism outside the passage.