كُلُّ مَا يَتَأَتَّى فِيهِ الِاسْتِعَارَةُ يَتَأَتَّى فِيهِ التَّشْبِيهُ مِنْ غَيْرِ عَكْسٍ
Where metaphor can be made, simile is possible; the reverse does not necessarily hold.
An explicit comparison can register a limited likeness even when the subject cannot convincingly be treated as belonging to the very kind represented by the image. Metaphor makes the stronger rhetorical claim by suppressing open comparison.
This principle concerns the effectiveness of metaphor. Deleting a comparative particle from any possible simile does not automatically yield a strong, successful metaphor.