Empty the bucket but keep the same sand and rocks. This time, fill the bucket with the sand first, and then try to place the rocks inside the bucket.
فَيَصِيرُ لَدَيْكَ دَلْوٌ مَلْآنٌ بِٱلْأَحْجَارِ وَٱلرَّمْلِ عَلَى ٱلسَّوَاءِ .‏