ما تـظـنه أسوأ ما حدث قد تكتشف فيما بعد أنه الأفضل لك علي الإطلاق......

_____
" ما " ( ma
in Arabic has several meaning and you can figure it out by the context 
1 ما = الذي (al de ) that ; which
2- ما = لم (not - expressing negation (lam
3- ما = ماذا (what (mada
4 ما = مُعين (some, a certain (moyan
and in that context it has the first meaning

"تظن "
1 تظن = think
2 تظن = suspect
and in that context it has the first meaning

الهاء في تظنه ـه (-u) Object pronoun
Singular him

"أسوأ " 'worst " aswa
"ما " that (ma)
"حدث " (happened (hadath
" قد " (may (qad
"تكتشف " (discover (taktashef
"فيما بعد" hereafter
" أنه " أن (that (ana
ه ـه u) him Object pronoun)
"الأفضل " (the best (al afdal
"لَكَ " لــ (to ( le
ك you masculine- Object pronoun ـكَ (-ka)

"علي الإطلاق " (At all ( 'la al etlaaq