Obstacle is the opposite of Benefit. Benefit is a synonym of Assistance. Assistance is a synonym of Aid. 
Moment is related to Chance. Chance is related to Option. Option is a synonym of Selection. Selection is a synonym of Survival. 
Obstacle <--Antonym--> Benefit <--Synonym--> Assistance <--Synonym--> Aid 
Moment <--RelatedTo--> Chance <--RelatedTo--> Option <--Synonym--> Selection <--Synonym--> Survival 